The PyTorch error on a Mac carries one number that people search for. This one is from a 16 GB Mac ( AudioLDM2 #20 ):

RuntimeError: MPS backend out of memory (MPS allocated: 18.02 GB, other allocations: 107.10 MB, max allowed: 18.13 GB). Tried to allocate 4.50 MB on private pool.

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In my earlier note I measured where it comes from on my 48 GB Mac. "max allowed" is PYTORCH_MPS_HIGH_WATERMARK_RATIO , 1.7 by default, times the GPU working set macOS recommends, which torch.mps.recommended_max_memory() returns. One machine can't tell you what that number is on the others, so I read it off other people's errors.

Where the numbers come from

On 24 October I searched GitHub for issues that quote the error with its "max allowed" value. That gave 250 issues and pull requests, 167 of them with a number in the text. Most values fall into a few groups, and where a reporter named their Mac's memory, the groups line up with the size.…